The International Bone Marrow Transplansplant Registry (IBMTR) is a collaborative study group that has been conducting research for the past 15 years in an effort to improve the safety and success of bone marrow translantation for the treatment of patients with a variety of otherwise incurable diseases. At present, 124 bone marrow transplant teams in the U.S. and abroad submit detailed information regarding their consecutive transplant experience to the IBMTR on uniform reporting forms. The IMBTR has detailed information on more than 3,700 recipients of allogeneic and syngeneic bone marrow transplants. Based on current accession rates, data for more than 6,000 additional patients is anticipated during the course of the planned investigations. In this five-year Program Project grant application, the Advisory Committee of the IBMTR requests support for a statistical Core Component that is required and shared solely within the proposed research program. Support also is requested to conduct studies designed to address and help resolve critical questions in two major areas of ongoing investigation. In project I, we propose to conduct scientific analyses investigating factors associated with success and failure following allogeneic bone marrow transplantation worldwide for both common and rare diseases including leukemia, aplastic anemia and genetic diseases. Further, we shall investigate factors affecting the outcome of bone marrow transplantation using donors than HLA-identical siblings. Project II is designed to identify risk factors associated with the major complications of allogeneic bone marrow transplantation including: acute chronic graft-vs- host disease, recurrent leukemia and interstitial pneumonitis.